R. Moshe Feinstein, in a set of halakhic letters penned in 1967 to R. Yosef B. Soloveitchik of Boston and to Dr. Bernard Lander (Igr. Moshe YD 3:43-44), unequivocally forbade Jewish participation in ecumenical dialogue with the Church, citing both concern for apostasy as well as inherent prohibitions of such dialogue. R. Feinstein was firm as steel that participation of any sort constituted grave infractions of Halakha.
In a series of halakhic and binding policy correspondence between 1962 and 1967 (published in Community, Covenant and Commitment), R. Soloveitchik articulated his unyielding position that Jewish delegations should not and may not take part in religious discussion with the Church. R. Soloveitchik expressed concern for apostasy and wrote that the Jewish and Christian religious differences and world outlooks are irreconcilable, such that discussion thereof would be wholly unfruitful and would be wrong.
Although, unlike R. Feinstein, R. Soloveitchik maintained that in theory, dialogue with the Church about “humanitarian and cultural endeavors” - universal, practical issues that do not touch upon personal religious beliefs and practices - would be acceptable and even positive (ibid. p. 260), the context of such dialogue in the situations addressed by R. Soloveitchik caused him to prohibit Jewish participation therein. R. Soloveitchik was adamant and unapologetic in his refusal to allow any form of personal religious discourse between Judaism and Christianity, and the circumstances and impressions conveyed by even otherwise permissible interchange compelled him to comprehensively ban such interchange in his correspondence.
R. Soloveitchik affirmed the same in his seminal 1964 essay Confrontation, in which he wrote in part:
…we must state, in unequivocal terms, the following. We are a totally independent faith community. We do not revolve as a satellite in any orbit. Nor are we related to any other faith community as "brethren" even though "separated."… For the mere appraisal of the worth of one community in terms of the service it has rendered to another community, no matter how great and important this service was, constitutes an infringement of the sovereignty and dignity of even the smallest of faith communities … Hence, it is important that the religious or theological logos should not be employed as the medium of communication between two faith communities … The relationship between two communities must be outer-directed and related to the secular orders with which men of faith come face to face. In the secular sphere, we may discuss positions to be taken, ideas to be evolved, and plans to be formulated. In these matters, religious communities may together recommend action to be developed and may seize the initiative to be implemented later by general society.
The Rabbinical Council of America, in a statement of addendum issued that same year, formally adopted R. Soloveitchik’s position as its official policy.
Later that year, R. Soloveitchik penned an open letter for publication in the Rabbinical Council of America Record, which reads in part:
We are, therefore, opposed to any public debate, dialogue or symposium concerning the doctrinal, dogmatic or ritual aspects of our faith vis-à-vis “similar” aspects of another faith community. We believe in and are committed to our Maker in a specific manner and we will not question, defend, offer apologies, analyze or rationalize our faith in dialogues centered about these “private” topics which express our personal relationship to the God of Israel.
It must be noted that these rulings of R. Feinstein and R. Soloveitchik were issued during and after the Second Vatican Council and Nostra Aetate, and that R. Feinstein and R. Soloveitchik never rescinded these rulings, despite official changes in Church policy toward Judaism and Jews during that period and the next several decades, throughout which R. Feinstein and R. Soloveitchik were alive and actively teaching and issuing halakhic and theological pronouncements. Direct family members of R. Soloveitchik have personally verified that R. Soloveitchik held resolutely to his rulings on these issues to the very end. R. Dovid Feinstein has affirmed that the positions of his father, R. Moshe Feinstein, pertain to these issues and remain in force to this very day, and R. Soloveitchik’s close disciples have likewise restated the firm position of R. Soloveitchik on these issues and their enduring relevance and applicability to the present and beyond. (Following a 2004 yeshiva visit by high-ranking Church clergy, R. Herschel Reichman, an intimate disciple of R. Soloveitchik, stated that R. Soloveitchik’s ban on interfaith religious discourse includes discussion regarding methods of religious study, even when the actual topics of study are not broached.)